The subject matter disclosed herein relates to a compression activated switch device for light emitting circuit boards, including light emitting diode (LED) circuit boards, activated by compression. More particularly, the subject matter relates to a compression activated switch device which provides electrical continuity under a predetermined amount of force applied during installation. Visual or audible feedback may be provided upon the application of the predetermined amount of force.
As solid state lighting systems have increased in usage, they have begun being produced in a greater variety of types of packages designed to suit multiple applications. Many of these systems include similar components, typically a light module (a circuit board containing at least one LED), a power supply or LED driver, a housing combined with or designed to connect to a heatsink, and some wiring and hardware. Many applications utilize a high power density. For instance, some LEDs operate at tens of milliamps (mA), while high power density LEDs may be driven at hundreds of mA or even over an ampere, requiring the use of a heatsink. Good thermal connection between the heatsink and the light module is important for operation of the light fixture within its design specification by allowing for sufficient heat dissipation.
Poor thermal connection between the light module and heatsink can result in multiple problems with solid state lighting devices. Some issues can include a reduction in performance, including a reduced lifetime of the light module, reduced efficiency of the system, and color shifting. Other issues can include a reduction in safety, such as exceeding the rated temperature of surrounding components and greater risk of failure.
In an effort to increase thermal connectivity between LED modules and heatsinks, the connections are often augmented with a thermal interface material (TIM) between the components. The performance of the TIM is highly dependent on a minimum thickness achieved by compression. Typically, a threaded fastener is employed to secure the LED module and the heatsink as well as to compress the TIM. Oftentimes a holder is employed to distribute the force of the threaded fastener onto the LED module. In using these components, a TIM manufacturer will often specify a minimum amount of compression in order to facilitate a good thermal connection. Further, a holder manufacturer will specify a fastener type and torque setting in order to achieve proper compression of the TIM or module. However, even following recommended practices during assembly, there is no practical method for verifying a sufficient thermal connection has been made.
For instance, a direct measurement of the pressure applied on a TIM is often difficult due to the inability to access the connection with an instrument. Indirect measurements such as temperature reading of the light module can take hours for the system to reach thermal equilibrium and the values can be heavily skewed by other factors. Thus, in most cases, compression is verified indirectly by confirming the fastener size and torque application. There are drawbacks to this method. Firstly, a torque screwdriver or other instrument is required and may be out of calibration. Secondly, the application of a specific torque on a fastener can produce a highly variable amount of compression. Contaminants or defects on the fastener thread, for instance, can increase the torque required to achieve suitable compression. A cross threaded condition can occur and bind the fasteners, which may result in a proper torque condition but with no compression on the TIM at all. Thirdly, the environmental conditions of installation may be less than ideal. The prior issues may be overcome within a factory assembly setting. However, in field service scenarios where the thermal connection between light module and heatsink is broken and then recreated during the installation of a replacement lamp unit, many of the aforementioned difficulties are amplified. In addition, installation can be affected by the skill of the contractor, location of the lighting system, the presence of contaminants, and whether the contractor has a particular and accurate torque wrench.